1. Field of the Invention
The present invention relates to a method for preparing an ocular article, and more particularly to a method for producing a silicone hydrogel with high water content.
2. Description of the Prior Art
So far, the contact lens has a development history of almost one hundred years, and is one of the important medical devices generally used by common lens population. In 1950s, a Czechoslovak scientist prepared a hydrogel by using poly(hydroxyethyl methacrylate) (HEMA), and invented a flexible contact lens, and this material is still being used now. With the progress of science and technology, the material of the contact lens also evolves towards high oxygen permeability and high comfort.
The contact lens made from a silicone hydrogel has a development history of many years. In the past, the development goals of the products were mainly focused on the improvement of the properties of the silicone hydrogel such as oxygen permeability and water content. Presently, the oxygen permeability of the silicone hydrogel products available in the market is up to 100 barrers or higher. However, the water content of the silicone hydrogel cannot be effectively improved.
Generally speaking, the silicone hydrogel consists mainly of a reaction product of a silicon-containing monomer and the water contained therein. The proportion of the water in the silicone hydrogel is also referred to as the water content of the silicone hydrogel. As the silicon-containing monomer and the reaction product thereof are hydrophobic and have a poor wettability, the contact lens made from the silicone hydrogel will have a poor surface wettability and a low water content, resulting in that the eyes tend to be dry and feel uncomfortable in wearing, which is the problem eagerly to be resolved in the current industry of silicone hydrogel contact lens.
In view of the problem of enhancing the water content and surface wettability of the contact lens, there have been improvements made by using various physical and chemical methods disclosed in the prior art. For example, U.S. Pat. Nos. 4,158,089 and 6,242,508 disclose adding other hydrophilic monomers to the formulation for co-polymerization; U.S. Pat. Nos. 5,969,076 and 6,596,294 disclose synthesizing various hydrophilic silicon-containing molecules by chemical methods and added the molecules to the formulation to improve hydrophilicity and wettability; and U.S. Pat. No. 6,367,929 discloses adding a high-molecular-weight hydrophilic polymer (such as PVP) to the main components of a silicone hydrogel to enhance the wettability and hydrophilicity. However, in terms of the technology status, these methods are less significant in effects for improving the water content of the silicone hydrogel, and the water contents are all less than 50%.
Moreover, there are also many researches on improvement of the water content or surface wettability of the contact lens by using physical methods. For example. U.S. Pat. Nos. 6,867,245 and 5,274,008 disclose using a high polarity mold in the preparation of contact lenses; and U.S. Pat. No. 4,214,014 discloses treating the surface of contact lenses with a plasma. Although these physical treatments may successfully improve the surface wettability of the contact lens, they cannot effectively enhance the water content of the contact lens itself, so that only a short-term comfort effect instead of a long-term comfort feeling can be obtained when wearing the contact lens improved by these methods.
In terms of comfort, the eyes always tend to be dry and feel uncomfortable after long-term wearing of the contact lens, and the underlying reasons include the higher water loss rate of the contact lens, the lack of sufficient tears provided by lacrimal gland, or the gradual water dissipation after long-time exposure of the contact lens to the air. Due to the above reasons, the wearers of contact lenses are likely to encounter the problems associated with dry eyes and even poor eyesight.
To sum up, there is still a need for a technical solution in the industry, so as to enable the contact lens formed by polymerization and molding to have a high water content and high water retention.